Why X-1 was built as a cruiser submarine

X-1 emerged from a longer British line of gun-submarine experiments, including the M-series, and took roughly four years from her November 1921 laying-down to 1925 commissioning. The cruiser-submarine concept answers a practical ammunition problem: torpedoes are bulky, expensive, and difficult to carry in quantity. X-1's four rapid-firing 5.2-inch guns and 400 rounds could dispose of merchantmen or light escorts while preserving torpedoes for capital ships and cruisers. A surfaced range of 12,000 nautical miles at 12 knots made the boat an ocean-going commerce raider able to appear far from British bases. The design therefore paired concealment with the endurance and gun ammunition needed to sustain attacks across distant sea lanes.